Conventional or prior art molding apparatus for continuously casting hollow bars commonly employ mandrels which are formed with pouring apertures or passages for receiving the molten metal to eventually be discharged in the space between the female die and the mandrel. Because of the space requirement in the mandrel to accommodate the pouring passages or apertures, the size of the mandrel in many cases does not permit the casting of hollow bars having relatively small internal diameters. Moreover, when pouring molten metal at 2100.degree. F., for example, molten copper, the mandrel becomes susceptible to heat damage, particularly if the mandrel is weakened by pouring passages or apertures. Such damage can, of course, require premature replacement of the die and mandrel which, of course, increases the cost of production. To avoid such damage, special metals or materials having a high melting point and strength at that point may be utilized, however, such special metals may significantly increase the cost of the mandrel. The latter factor becomes more serious when it is considered that mandrels and dies must be replaced on a periodic basis due to the high temperature encountered in use. Also the down time and labor will increase the cost of the casting operation.
Pouring passages or apertures in the mandrel such as used in prior art or conventional die assemblies suffer from the further drawback that they are susceptible to clogging by solidification of the molten metal which is to be cast into the hollow bar. Clogging of the inlet passages or apertures in the die assembly, if unchecked, can cause overflow of the molten metal which presents a most dangerous situation from the standpoint of safety. It also can damage other parts of the casting apparatus contacted by the overflowing molten metal. This becomes very important, for example, when casting hollow copper billets to be used for extruding copper tubing where the production rate may be as high as 8,000 to 12,000 billets per hour.
Another common characteristic of mandrels of the prior art or which are conventionally used in the trade, is that they often are composed of multiple parts which create spaces in the joints between the parts. Should any molten metal enter the spaces, it can cause rupture or deformation of the mandrel requiring replacement or resulting in eccentricity of the mandrel. Moreover, such mandrel assemblies are difficult if not impossible to replace during a commercial on-going casting operation. In addition, multiple piece mandrels can present problems in cooling the mandrels during casting.
Examples of apparatus which suffer from one or more of the drawbacks mentioned above are disclosed in U.S. Pat. Nos. 3,331,430, issued July 18, 1967, 3,735,803, issued May 29, 1973 and 3,710,840, issued Jan. 16, 1973.